ok im curious on this now. My truck has the manual locking hubs to put it into 4x4. and then the auto button to engage it. if the hubs are not locked in, will the switch put it in 4x4 mode or not, ...
I had an '04 F350 FX4. I just left the hubs in auto. As stated above, when I engaged 4x4 inside, the hubs automatically engaged. They never failed so I never had to use the manual engage function.